Actually, I think both Huxley and Kropotkin drew inferences from Darwin's work that Robin believes to be reasonable. That is, contrary to your conclusion, I think that Robin thinks that Huxley and Kropotkin are both "compatible" with Darwin, and that it is still an open question. To quote Robin again:
Human nature was not forged in the anvil of known human history
but rather under the neolithic conditions of prehistory about
which we know far less. Were these conditions more likely to
"select" individually aggressive traits or traits that enhanced
effective cooperative behavior?
If the answer to this question is not obvious, and if particular
social institutions developed during recorded history would have
elicited antisocial behavior even from people with sociable
genetic dispositions, there is no more a priori reason to suppose
that the "laws of evolution" have doomed us to be Hobbesian
combatants than altruistic saints.
Does that clear things up any?
Bill